Low, Slow building boost?

[crick]

I've got a friend's 1987 GN and we are having trouble figuring out what is wrong with it. The car used to be very fast and now its pretty much a terd. The car has like 12k original miles. roughly 1k miles on the new turbo.

The car is very slow to build boost and only builds to about 10psi. We pulled the turbo off and had it looked at by a very reputable turbo shop in town and the guy said there is absolutely nothing wrong with the turbo.

So, I'm trying to diagnose what could be causing this. The engine has a nasty rattle on the passenger side. When the engine is cold you can't hear it, then when its hot the rattle is very noticable. the rattle is not coming from the valve train or the inside of the motor. It sounds like a noisy heat shield but i could be wrong. I would love for it to be a cracked manifold because that would cause the boost issues but I don't hear the typical cracked manifold exhaust leak sounds.

I asked my friend if he could make a connection between the onset of the rattle and the decline in performance and he said no. However, this car has rarely been driven in the past few years.

Any insight would be very helpful. I just wonder if I should chase down this rattle or if it is typical of GN's and not a major issue?

 

[SlickTR]

I've got a friend's 1987 GN and we are having trouble figuring out what is wrong with it. The car used to be very fast and now its pretty much a terd. The car has like 12k original miles. roughly 1k miles on the new turbo.

The car is very slow to build boost and only builds to about 10psi. We pulled the turbo off and had it looked at by a very reputable turbo shop in town and the guy said there is absolutely nothing wrong with the turbo.

So, I'm trying to diagnose what could be causing this. The engine has a nasty rattle on the passenger side. When the engine is cold you can't hear it, then when its hot the rattle is very noticable. the rattle is not coming from the valve train or the inside of the motor. It sounds like a noisy heat shield but i could be wrong. I would love for it to be a cracked manifold because that would cause the boost issues but I don't hear the typical cracked manifold exhaust leak sounds.

I asked my friend if he could make a connection between the onset of the rattle and the decline in performance and he said no. However, this car has rarely been driven in the past few years.

Any insight would be very helpful. I just wonder if I should chase down this rattle or if it is typical of GN's and not a major issue?

Any more info you can provide? Anything happen before this issue started? Is this a stock turbo and stock wastegate setup? Sounds like it could be the wastegate not closing, I suppose it could be a major exhaust leak or one hell of a boost leak. Take a look at the wastegate, look for exhaust leaks, loose/blown off intercooler hoses etc...and related or not, I'd find out what that rattle is, these cars are old and can noisy lol, but that doesnt sound like its a normal noise.

 

[SHADOWII]

You have a .......

cracked drivers side header, between #'s 3 & 5. The crack can cause a buzzing sound and the rattle may be the broken weld on the heat shield. It is usually a hairline crack that expands while heating and very difficult to see from the outside. I had to take mine off and see a whitish line on the inside to find it. The 10#s is a typical symptom. Hope this helps.

 

[Chuck Leeper]

Time to scan it...
Cat plugged up?

 

[crick]

Any more info you can provide? Anything happen before this issue started? Is this a stock turbo and stock wastegate setup? Sounds like it could be the wastegate not closing, I suppose it could be a major exhaust leak or one hell of a boost leak. Take a look at the wastegate, look for exhaust leaks, loose/blown off intercooler hoses etc...and related or not, I'd find out what that rattle is, these cars are old and can noisy lol, but that doesnt sound like its a normal noise.

aftermarket turbo. we swapped out the wastegate and it didn't help. i suppose it could still not be closing all the way. i need to look at that more closely. we have double checked all the intercooler piping and hoses on the boost side of the turbo and everything is tight.

i talked to another guy last night who has spent some time around the car and he said he always remembers the rattle being there even when the car was running good.

as far as we know, nothing happened before the issue started. like a said, this car spends most of its days in storage and i think one day he went to drive it and it just wouldnt boost.

cracked drivers side header, between #'s 3 & 5. The crack can cause a buzzing sound and the rattle may be the broken weld on the heat shield. It is usually a hairline crack that expands while heating and very difficult to see from the outside. I had to take mine off and see a whitish line on the inside to find it. The 10#s is a typical symptom. Hope this helps.

do you mean passenger side? i thought it could be a cracked header/manifold but the more i thought about it the more i think its just a heat shield rattling. the car doesn't really make any of the characteristic exhaust leak sounds. later on today i am going to start it up and let it warm up, when it starts rattling i will record the sounds and post it on here.



could a vacuum leak be the culprit of the low boost?

 

[crick]

Time to scan it...
Cat plugged up?

no cats on this car.

what do you mean when you say scan it? it's got a scanmaster on it but i don't know what most of the readings mean. i guess i need to study up on that.

 

[Underboost]

What's the fuel pressure at the regulator? A rich fuel mixture will definitely give you a slow spool.

 

[crick]

i'm not sure what the fuel pressure is. i know its a little rich. the car smokes a little at idle from where it spits fuel. does the scan master give an afr reading?

 

[just plain john]

could a vacuum leak be the culprit of the low boost?

Yes it could.

 

[crick]

i might try hooking up a vac gauge before i start searching for a leak. what kind of vacuum should i expect at idle. the internals on this motor are all stock. should i see nearly 20 in. hg. of vac?

 

[jasjamz]

i might try hooking up a vac gauge before i start searching for a leak. what kind of vacuum should i expect at idle. the internals on this motor are all stock. should i see nearly 20 in. hg. of vac?

On stockers I see 15(avg)-18(best)in of vac

 

[forzfed]

Did you check your boost solenoid? Was the rattle present before you took the turbo off? Because if it wasn't you might have a loose down pipe. With 12k on the car, I wouldn't think the headers are cracked, but I guess anything is possible. My one car has 14k and ripped off low 12's and my headers still have some of the factory black paint left on the headers and look perfect.

 

[crick]

yeah the rattle was there before we took the turbo off. it didn't rattle for about 30min after we put the turbo back on though. then it started again.

where is the boost solenoid and what does it do?

 

[forzfed]

The boost solenoid is locate on the front of your passenger side valve cover. It usually fails safe, which would give you around 9-10psi of boost. It has the hoses that connect to the waste gate and T off to the turbo, might want to check to make sure the hoses aren't rotten. Definitely find where that rattle is coming from.

 

[crick]

i was wondering what that was. i thought it was some kind of sensor. i bypassed it completely the other night and it didn't effect the performance at all. still crappy.

also, on this car... the boost solenoid appears to have two places to attach vacuum line, i assume for pass through? which makes sense after reading a description of how a boost solenoid operates. However, on this car, one of the nipples is capped and the vac line only attaches to one of the boost solenoids nipples.

any enlightenment here?

 

[RIFF RAFF]

Witch side

i was wondering what that was. I thought it was some kind of sensor. I bypassed it completely the other night and it didn't effect the performance at all. Still crappy.

Also, on this car... The boost solenoid appears to have two places to attach vacuum line, i assume for pass through? Which makes sense after reading a description of how a boost solenoid operates. However, on this car, one of the nipples is capped and the vac line only attaches to one of the boost solenoids nipples.

Any enlightenment here?

ones a vent with a filter the other is to the turbo. take the cap off this might just be your problem . the one closest to the fender goes to the turbo .

 

[crick]

ones a vent with a filter the other is to the turbo if the one thats broke is closet to the fender you will need a new or replacement .i have a used one if needed ..

ok, that makes sense. how important is the filter? there was traces of some deteriorated foam on what i thought was a vac cap on the boost solenoid. so i have no filter.

this car has a .60 trim turbo, 60lb injectors, and art carr tranny. i didnt say that before, but it should be making twice as much boost as it is. idle afr reading on the scanmaster is 7.

this is the first turbo buick ive worked on so i don't know any car specific things. I'm learning as i go. its tricky because i have to factor in how much time this car spends just sitting. i don't know if the injectors are gummed up or what. but i wouldnt think that is the case since it seems to be running pretty rich at idle.

could a transmission issue cause the motor to not build boost properly? the transmission doesn't seem to let the motor rev very high before it shifts.

 

[RIFF RAFF]

see here

used one for example

 

[RIFF RAFF]

the foam

was from the oe filter . they didnt last long .. and take the cap off

 

[crick]

Thanks for the pics that really helps me. i will get rid of the oe filter piece and do something similar to what you have shown me.

i'm going to get out there and check the vacuum pressure and work on that boost controller after dinner. i'll take some pictures of what i end up with. hopefully i can just pick up one of those tiny filters at the auto parts store.